I would like to know that is it really necessary at this stage to make our under development apps compatible with iOS6 and iPhone5. I am developing an iPhone application which is in final stage. With in 10 days I have to submit it to the app store. So, if it is necessary to make our present/under development apps compatible with iOS6 and iPhone5, what steps should be taken? And if it is not that necessary, then what other precautions should I take?
You need to use Xcode 4.5 GM. For the new resolution to be enabled on iPhone 5 and new iPod, you need to provide a launch image at the appropriate size. You also have to make sure that you views are resolution independent and resize correctly. You can test on the simulator.
Since you'll be using the new Xcode, you might as well "modernize" your code to use the new Objective C literals syntax for arrays, dictionaries and NSNumber objects. This will make your code much more readable (this is probably debatable, but that's my opinion).
These are compiler additions, and should work for any iOS target.
Other SDK additions, such as auto-layout support, will be probably irrelevant for you as you will want to target older iOS devices as well for now. But it is worth taking a look at the documentation to be familiar.
There are changes to the autorotation flows with views and windows. Again, check the documentation for the changes and how to prepare for iOS6.